Electric heating apparatus



April 23, 1929. D G, PEWE '1,710,511

ELECTRIC HEAT TNG APPARATUS Filed March l5. 192]? 2 Sheets-Sheet l April 23, 1929. D. G. PETRIE ELECTRIC HEATING APPARATUS Filed March l5. 1928 2 Sheets-Sheet 0.6;. FETT/'e @wwwa/lm Patented Apr. 23, 1929.

UNITED STATES PATEN GFFICE.

DAVID GRANT PETRE, OF 13 XLEY HEATH, ENGLAND, ASSIGNQ'R EO YOUNG, SMOND, & YUNG, LMITED, OF BEXLEY HEATH, ENGLAND, A BRETISH COMPANY.

:ELEC'JRC HEATNG APPARATUS.

Application led March 15, 1928, Serial No. 281,994, and in Great Britain March 21, 1927'.

This invention relates to electric heating apparatus ot the type wherein a me, such as a tube, carries a resistance unit comprising a heat-resisting insulating base o'f strip form, and an electrical conductor constituting a resistance element so mounted on said base to be insulated from the frame. 'lhe invention has for its main object to pr vide resistance unit ol improved construction 'lor apparatus ot this type, in order to facilitate the construction and erection oit the apparatus, which may be used for heating rooms or as an immersion heater or otherwise.

According to an important teature el the imiention, there .is provided in or 'for electric heating apparatus of the type described, a resistance unit having metallic edging that extends along one or both longitudinal edges oit the base ot the unit, for example i mica, and is electrically connected to the resistance element, inorder that the metallic edging may serve as a return Wire for current passing through the resistance element, ann thereby obviating the use ot' a separate return Wire to a terminal at one end ot the heater.

According to another feature of the invention, a resistance unit as described in the preceding paragraph is combined with one or more insulators carried by it and arranged to insulate the frame from the metallic edging that serves as a return conductor.

According to another in'iportant feature of the invention, there is provided in or 'lor electric heating apparatus ot the type described, a resistance unit comprising a base in the Ylorm et a plurality ot pieces ot insulation (e. g. mica) of strip form arranged endto-end, and metallic edging extending along one or both of the longitudinal edges the pieces of insulation and servingl to hold the same together, in combination With an insulator, or a plurality of insulators spaced apart, mounted on the resistance unit and arranged to insulate the metallic edging from the frame, for the purpose et supporting the resistance in the trame and improving the insultion or the resistance element.

Conveniently, each insulator a'l'oresaid is in tie term of a plate, Yfor example et mica, that the construction or ine insulators mounted on the resistance unit.

The invention also provides electric heatmg apparatus ot the type described above comprising a resistance unit in any or the forms set forth above.

The invention is illustrated diagrammatically and by Way oit example in the accompanying' drawing, wherein igure 1 is a longitudinal section lthrough part of an electric heater according' to the invention comprising an improved construe-- tion of resistance unit, and

Figure 2 is a vertical cross-section taken on the line in Figure l;

Figure 3 is an elevation of a resistance unit according to the invention provided with varions forms oit insulators, and

Figures l and 5 are vertical crossssections taken respectively on the lines l-d and 5 5 in Figure 3;

Figure il is a longitudinal section through part oif an electric heater provided with auother i'orm of resistance unit and insulator according to the invention and Figure Z is a vertical cross-section take on the line 7 7 in Figure 6.

Lilie reference characters designate like parts tlnoughout the several views.

Referring lirst to Figures l and 2, an electric heater comprises i, traine in the torni or a single metal tube, or a number oi such tubes connected end-to-end, which provide a continuous tubular passage l() that is closed at one end by a cap ll. rlhe other end oi the pesage, not shown, may carry au insulating hlocl; having' two terminals, which block and terminals are preferably enclosed hy a cap on the adjacent cad et the tube or tubes.

A resistance unit in strip il.E rm comprises a hase consisting oi? rectangular mica plates l2 arranged end-to-end, and metallic edging 13 ot ll-section connectingv the plates together at their edges. This structure extends .troni end-to-end of the passage and carries a resistance elem-eut in the form ot a coiled resistance vire thieaded through holes in the mica base constituted by said plates 12. As described so tar this resistance unit is known in itsel'l".

In a preferred term o't construction ot electric heater according to this invention, the resistance unit is insulated from the walls et the heater, and one terminal aforesaid has the adjacent end et the resistance Wire 14 electrically connected to it and the other end oi the Wire is electrically connected to one or bot-h metallic strips 13 which are electrically connected to the other terminal aforesaid. This construction of heater is a very simple one as there is only a single length of rcsistance wire and only one row of perforations in the `'ii-ca base, andL no return wire is required although the two terminals are both at the same end of the heater.

Various forms of insulators for insulating the metallic edging from the outer tube or tribes will now be described, insulation 15, for example a mica disc or washer, being preferably interposed between the cap 11 and the adjacent ends of the metallic edging 13. As shown in Figures 1 and 2, an insulator in the form of a rectangular sheet- 2() of mica or other convenient insulatingr rnat-erial is ar'- ranged between the adjacent ends of two of the plates 12 and constitutes part of the base of the resistance unit. This sheet has at its ends semi-circular lugs 21 which extend through slots in the metallic edging 13 and constitute spacing pieces for spacing the latter away from the surrounding tube or tubes.

In a modified construction of insulator shown in Figure 1, two sheets of mica or the like, one at each side of the plates 12, are riveted together' by eyelets 23 and have their ends 24 extending beyond the edging 13. These extending ends 24 are preferably curved so as to present convex edges for bearing against the adjacent outer tube, whereby the insertion of the resistance unit in the outer tube is facilitated, as friction will be reduced, as is the case also with the lugs 21. In some cases only one sheet 22 may be uset. The resistance wire may be threaded through the hollow rivets 23 and also through a. perfo 'ation in the sheet 20, as illust-rated.

In Figure 3 the insulator shown at the extreme left-hand of the figure differs from that just described in the preceding paragraph only in that additional rivets 34; which may be hollow are provided securing the sheets to the metallic edging 13, a washer 25 boing provided between the end of each rivet 34 and the adjacent sheet 22. These rivets lend rigidity to the insulator.

The construction of insulator' shown in Figures 3 and 4 differs from that described in the preceding paragraph in that channel-shaped metal reinforcing elements 26 are used instead of the rivets 34 and serve to secure the ends of the sheets 22 to the metallic edgingl 13 and also to reinforce the sheets 22 against bending stres: acting transversely of the length of the sheets. These elements 2G are slotted each between their ends which are riveted to the metallic edging and serve also to reinforce the resistance unit against bending in the direction of its length.

The insulator' shown in Figures and 5 differs from those described above comprising sheets 22 in that it is reinforced against bend ing stresses acting in the direction of length of the plates by a metal reinforcing element 27 of strip form threaded through two slots 28 in one of the plates 22 and having its ends bent on themselves and lying each in a recess 29 at t-he ends of the plates 22 which are thereby grippcd and firmly held in position. rl`his clement 27 thus also serves to reinforce the resistance unit against bending stresses acting transversely of its length.

In each of the constructions of insulator de scribed above the length of the insulator is preferably equal to the internal diameter of the containing tube so as to hold the resistance unit lying diametrically across the tube. If additional support required, for example in a tube of larger diameter, say a three inch tube, as shown in Figures G and 7, the sheets 22 may have squared ends and carry on the same spring clips 30 of the form shown having laterally exten ding wings which will bear against the inner wall of the tubular passage 10 at both sides of the resistance unit. Such clips serve as locating means for positioning the resistance unit diametrically or substantially dianietrieally in the outer' tube, and also serve as reinforcing means for the sheets 22 against bending stresses acting transversely on them. These clips 30 may be secured in posit-ion by rivets 31 which hold the adjacent ends of the sheets 22 firmly together. In some cases, particularly if the tubular passage 10 is short, only one such insulator need be provided.

The resistance element may be arranged in any convenient manner, for example rectilinearly, or zigzag, on the mica base. lf desired, the resistance element may extend from end-to-end of the unit and be doubled on itself, the bend of the wire boing connected electrically to the metallic edging. In this case three terminals will be provided, a separate control preferably being provided for each of the two connected to the element.

An important advantage of the invention is that it permits narrower strips of mica to be used than heretofore, whereby a considerable saving in cost of manufacture is effected. Even if the resistance element is not electrically connected to the metallic edging, which will then not serve as a return conductor, the improved construction of resistance unit provided with supporting insulators as described above has the advantage that the insulation of the resistance element is enhanced because even if for any cause, say owing to sagging, the element contacts with the metallic edging at one point, the circuit will not be put to earth.

Various modications may be made in the details of construction described above without departing from the scope of the invention as delined in the claims. For example, other' insulating materials besides mica, such as glass, earthenware and the like may be used for the base in certain eases. Also, a supporting insulator as described may be reinforced both longitudinally and transversely, for example by elements such as 26 and 27.

I claim:

l. For use with electric heating apparatus, a resistance unit comprising a heat-resisting insrlating` base ot strip form, an electrical conductor constituting a resistance element mounted on said hase, and metallic edging that extends along at least one longitudinal edge of the hase, is electrically connected to the resistance element, and serves as a return conductor.

2. For use with electric heating apparatus, a resistance unit comprising a heat-resisting insulating base ot strip form, an electrical conductor constituting a resistanceelement mounted on said base, and metallic edging that extends along at least one longitudinal edge ot the base, is electrically connected to the resistance element, and serves as a return conductor, in combination with at least one insulator carried by said resistance unit 'for insulating the latter from the traine oit the apparatus. I

3. For use with electric heating apparatus, a resistance unit comprising a base in the forni of a plurality of pieces of insulation oic strip torni arranged end-to-end, an electrical conductor constituting a resistance element mounted on said base, metallic edging extending along at least one of the longitudinal edges ot the pieces of insulation and serving` to hold the same together, and a plurality ot insulators spaced apart and mounted on the resistance unit 'llor insulating the latter 'from the trame of the apparatus.

1l. For use in electric heating apparatus, a resistance unit comprising a heat-resisting insulating base oit strip form, an electrical conductor constituting a resistance element mounted on said base, and metallic edging that extends along at least one longitudinal ed oil? the hase, and is electrically connected to the resistance element, and serves as a return conductor; and an insulator of plate form that is mounted on said resistance unit, and lies transversely ot the direction ot length of the latter, and extends beyond each longitudinal edge thereof provided With metallic edging.

5. For use in electric heating apparatus, the combination ot a resistance unit comprising a heat-resisting insulatingl base of strip torni, an electrical conductor constituting a resistance element threaded through said base, and metallic edging that extends along at luist one longitudinal edge ot the base, and is electrically connected to the resistance element, and serves as a return conductor; an insulator in the form ot a. thin plate that is mounted on said resistance unit, and lies transverse v of the direction of length oi the latter, and extends beyond each longitudinal edge thereot provided with metallic` edging, and reinforcing means arranged to reinforce said insulator against bending stresses.

6. For use with electric heating apparatus, a resista ce unit comprising a heat-resisting insulating hase ot strip torni, an electrical conductor consi tilting a resistance element mounted on said base, and metallic edging that extends along at least one longitudinal edge ot the base, is electrically connected to the resistance element, and serves as a return coruluctor; and an insulator' comprising two sheets ot thin insulating' material placed one at each side ot the base and riveted together through the latter and extending beyond each longitudinal edge oll llie base provided with metallic edging.

i. For use with electric heating apparatus, the combination ot' a resistance unit comprising a lrent-resisting` insulating base ot strip torni, an electrical conductor constituting' a resistance element mounted on said base, :ind metallic edging that extends along at least one longitudnial er c of the base, electrically connected to the resistance element, and serres as a return conductor; an insulator comprising two sheets ol thin insulating material placed one at each sine ot the base and riveted together through the latter and extending beyond both edges of the base, and two spr =j clips mounted one on each end ot' the insulator'.

8: rin electric heater comprising in combination a metal il in the 'form oli a tube, and a resistance unit therein, which resistance unit comifirisis a .heat-rcsistii'ig insulating hase oi strip forni, an electrical conductor const tuting a resiiiitancc element mounted on sai-l ase and metallic cdoing that extends along at least one longiti linal edge ot the base, is electrically connected tothe resistance element, and serves as a return conductor.

l). An electric heater comprising in couiliination a inelal irsnie in the torni ot a tube, andare tance unit therein, which resistance unit compris is an insulating base ot thin inaterial in strip form, an electrical conductor constituting a resistance element threaded through the said base and extending :trom end to end thereof, metallic edging that eX- tends along both longitrulinal edges oit the base, is electrically connected to the resistance element. and serves as a return con ductor, and. a plurality ot insulators mounted on said resistance unit in spaced relation along the saine, each ot which insulators comprises two sheets ot thin insulating material. placed one on each side of the base and riveted together' through the latter and extending beyond the metallic edging on both edges ot the base.

In tcsl'iniony whereof I a'liix my signature.

DAVlD Gli-ANT llETRl'E. 

